THF is a commodity in the chemical industry, widely used as a solvent and as an intermediate in the preparation of various polymeric glycols useful in preparing polyurethanes.
One of the several methods used to commercially prepare THF is a three-step process which employs acetylene and formaldehyde as starting materials. In the first step of that process, acetylene and formaldehyde are reacted to form 1,4-butynediol, using a copper-acetylide complex as the catalyst. This reaction is described in U.S. Pat. Nos. 3,560,576 and 3,650,985, both to J. R. Kirchner.
In the second step, the butynediol formed in the first step is catalytically hydrogenated to 1,4-butanediol, using a Raney nickel catalyst. This procedure is described in British Pat. No. 1,242,358.
In the third step of that process, the butanediol from the second step is catalytically dehydrated and cyclized to THF using sulfuric acid as the catalyst, as described in U.S. Pat. No. 3,726,905 to J. S. Coates and V. J. Reilly.
The THF produced in that way is crude and must be refined if it is to meet commercial standards. This is commonly done by multi-step distillation.
Distillation is a generally satisfactory way of refining THF, except that the crude THF contains water and formic acid which attack and corrode the carbon steel of which distillation columns are ordinarily constructed. This corrosion can be controlled by eliminating the formic acid with base, and this is ordinarily done by simply adding large amounts of base to the crude THF. This excess of base, however, causes the formation of methacrolein, whose presence causes color formation in polymeric glycols made from the refined THF.
It is, of course, highly desirable to minimize this corrosion and to hinder the formation of methacrolein.